This invention relates generally to a composite type collapsible tube and more particularly to an improved collapsible tube having no side seam and methods of manufacture.
Most known extruded metallic tubes are manufactured by impact extrusion, and have barrel section wall thickness ranging between 100 and 150.mu.. This value of wall thickness has been selected as being optimum from a viewpoint of the packing characteristics of the product tubes. Too large a wall thickness will deteriorate the characteristics of the tube for pressing out the content, and increases the cost of production; and too small a wall thickness often causes difficulties in the production process for avoiding pin-holes, wrinkles, dents and other inconveniences which may be derived from too small a wall thickness. Further, these known metallic tubes are undesirably corroded by the contents when the content exhibits acidity or alkalinity. In addition, due to the plasticity of the metallic material, the tube cannot have restoring or recovering characteristics, often resulting in breakage of the tube allowing the content to leak out of the tube.
To overcome these problems or shortcomings, various attempts have been made up to now. However, unfortunately, no successful attempt has been made which can completely overcome these problems inherent in the extruded metallic tube.
More specifically, it has been proposed to improve the nature of an inner resin coating or the inner coating method itself, so as to increase the chemical stability of the inner surface of the tube against an acidic or alkali content. At the same time, attempts have been made to fit shrink tubes or to apply shrinking paint, in order to improve the recovery characteristics of the tubes. However, these proposals and attempts are still insufficient and can not be put into practical use.
Conventionally, as a countermeasure for preventing breakage of the tube due to dents or bends, the wall thickness has been increased to some extent, and the metallic material is made to undergo sufficient annealing. Thus, it is contrary to conventional technical ideas to reduce the thickness of the metallic layer, especially at the barrel section of the tube. Rather, thinning of the wall has been considered as a cause for deterioration of the tube characteristics. This state of the technology is established by the fact that all of the considerable number of prior art proposals up to now fail to teach or suggest the thinning of the metallic tube wall, especially at the barrel portion, as far as the present inventors know. At the same time, it is to be pointed out that no prior art has been found through a search conducted by the present inventors, concerning a method for producing metallic tubes having a barrel section thickness as small as 70.mu. or less. In fact, no thin-walled metallic tube has been developed up to now. A study has not been made as to the thinning of the metallic tube wall, because it is commonly accepted that a thin wall inevitably leads to deterioration of mechanical strength.
Plastic tubes and laminate tubes have become popular recently, because they are free from some of the above described problems inherent in the metallic tubes. However, the plastic tube often results in a change of weight of the contents or degradation of the contents, due to its poor barrier properties. At the same time, the recovery force of the plastic tubular structure is too strong so that air is sucked in and stays in the tube, resulting in a further degradation of the contents or difficulty in pressing out the contents.
Turning to the laminate tubes, the most commonly adopted production process includes the step of seaming a laminate film, such as a metal foil into a tubular form, attaching a neck portion to the tubular body by means of injection molding to form a press-out tube. This process inevitably causes a side seam in the tubular barrel section, often resulting in leakage of the content due to peeling off at the side seam. In addition, the gas-barrier property of this tube is not sufficiently reliable, especially at the neck and shoulder portions of the tube. The side seam inconveniently deteriorates the appearance of the product tube. Further, for obtaining a good heat-seam at the barrel portion and good workability or shaping characteristic of the shoulder portion, the resinous material to be used is limited only to the thermoplastic resins. At the same time, since the neck portion constitutes only resin, the wall thickness at the neck portion has to be considerably large in order to provide a sufficient barrier property. Furthermore, the nature of the contents accommodatable by this type of tube is limited or restricted from a viewpoint of chemical stability. The use of the tube for holding a material which requires heat sterilization is prohibited, because the side seam of the barrel section may be broken as it is subjected to a high temperature in the course of the heat sterilization.
With respect to the recovery characteristic of this type of tube, it is extremely difficult to obtain the desired recovery characteristics through an adjustment or preparation of layers. A reduced recovery force is obtainable by thickening the layer of metallic material which tends to exhibit a plastic deformation, such as aluminum foil. However, in conventional laminate tubes, aluminum foil is used not for the purpose of adjusting the recovery characteristics, but rather for the purpose of improving the barrier property of the product tube. In addition, thickening the plastically deformable layer does not directly lead to the thinning of another layer or layers. In other words, the other layers may not be thinner, even when the thickness of the plastically deformable layer is increased. Otherwise the desired chemical stability against the contents and the protecting characteristics of the tube against external conditions will not be obtained. This means that the total thickness of the tube is inconveniently increased. Consequently, the bonding strength at the side seam and/or end seal portion is lowered, allowing the contents to escape from the tube.
Accordingly, it is desirable to provide a composite collapsible tube which is entirely free from the above noted shortcomings or drawbacks of conventional metallic tubes, laminate tubes and plastic tubes, while preserving and making use of the advantages of these tubes.